New research published in BMJ Mental Health illuminates the connection between lifelong cannabis consumption and brain health among middle-aged to older adults. The research revealed that people who have used cannabis show variations in their brain structure and functioning when contrasted with those who haven’t used it, notably concerning aspects like the integrity of white matter and how different parts of the brain connect within networks. Nevertheless, sophisticated genetic examinations suggest these discrepancies probably do not stem directly from using cannabis, implying that additional elements might be influencing these outcomes.
Over the last ten years, there has been a significant rise in cannabis consumption amongst elderly individuals, partly due to its legalisation for both medicinal and recreational uses across numerous areas. Even though it has become more widely accepted, studies examining the prolonged impacts of cannabis on cognitive function within ageing communities remain scarce.
Current research largely concentrates on young people and frequent users, thus leaving many uncertainties regarding its effects on elderly occasional consumers. Moreover, earlier investigations have found it challenging to ascertain if the detected alterations in the brain can be solely attributed to cannabis consumption or if they are affected by additional variables. This latest study sought to bridge this gap by integrating conventional observation techniques with genetic analysis to investigate the possible causative link between cannabis usage and neurological well-being.
"As cannabis usage increases worldwide following its legalisation for both medicinal and recreational uses, there is an increasing necessity to comprehend its possible impacts on the brain, especially among elderly individuals," stated the study’s lead author. Saba Ishrat A PhD student in psychiatry at the University of Oxford stated, "Although maintaining brain health in later years is crucial, elderly individuals have frequently been overlooked in cannabis studies. This research represents the most extensive observational analysis conducted so far to investigate how cannabis usage correlates with changes in brain structure and functionality. Additionally, this is the pioneering effort to integrate genetic information for exploring possible causative relationships."
The investigators examined information from 15,896 individuals enrolled in the UK Biobank, an extensive health resource. These participants, who were between 40 and 69 years old when the research began, submitted details concerning their past usage of cannabis through self-reports. Those who used cannabis were grouped according to how often they consumed it, distinguishing those classified as low-frequency users (with 1–10 instances) from high-frequency ones (those consuming 11 times or above). The collection of brain images was conducted employing sophisticated MRI methods, which assessed more than 3,900 aspects linked to both the form and operation of the brain.
The research concentrated on the integrity of white matter, evaluated via fractional anisotropy and mean diffusivity, along with functional connectivity within various brain networks including the default mode network and the central executive network. The analysis contrasted these metrics between individuals who use cannabis and those who do not, adjusting for possible influencing variables like age, gender, educational background, and psychological state.
Users of cannabis displayed notable variations in their brain measurements when contrasted with those who do not use the substance. These discrepancies were most evident in the quality of white matter, specifically within the genu of the corpus callosum—a part that links the brain's left and right halves. Individuals using cannabis had decreased fractional anisotropy and increased mean diffusivity in this area, suggesting diminished white matter integrity. Comparable trends were also noted in various other white matter pathways, such as the cingulum bundle and the anterior corona radiata.
The functional connectivity studies indicated either diminished or enhanced links among different neural networks, notably within areas linked to the default mode network and the central executive network. These networks play key roles in functions like making decisions, retaining memories, and focusing attention. Some parts of the brain exhibited heightened interconnectivity, whereas others experienced decreased connectivity, implying a multifaceted and inconsistent effect of cannabis consumption on cognitive processes.
In order to delve deeper into causality, the scientists employed Mendelian randomisation, an approach which utilises genetic information to establish cause-and-effect connections. Even though certain correlations were noted, the genetic studies did not provide any indication of a causal link between cannabis consumption and alterations in brain architecture or operation. Consequently, this suggests that the detected variations might be due to external influences like habits, economic standing, or additional aspects of well-being, instead of stemming directly from cannabis usage itself.
In our research, we discovered an association between lifetime cannabis consumption and various indicators of brain structure and functionality in subsequent years, such as diminished white matter integrity and decreased resting-state functional connectivity within certain areas of the brain," Ishrat stated to News, Diwdia-. "Nevertheless, our genetic examinations did not confirm a direct causative relationship, indicating that these noted correlations might not be solely due to cannabis usage.
One unexpected finding was the absence of replicated connections between cannabis usage and the size of grey matter in the hippocampus—a crucial area for memory—when compared with previous reports. This discrepancy might stem from variations in participant ages, since past research concentrated on teenagers and young adults, but our study included individuals who were middle-aged to elderly. Additionally, it is plausible that alterations in white matter may be more responsive to the impacts of cannabis than measurements related to grey matter.
Like all studies, this one comes with certain limitations. The participants from the UK Biobank tend to be healthier and better educated compared to the broader public, potentially affecting how widely applicable these results can be considered. Furthermore, due to insufficient statistical power, the Mendelian randomization analyses might not have detected minor causal relationships effectively. Finally, because only a few individuals reported frequent marijuana usage within the dataset, examining specific impacts based on varying levels of consumption was challenging for the investigators.
“We should approach our conclusions with care,” Ishrat stated. “The unrecorded factors within the observational study could clarify why we see differences when comparing this data to our genetic analysis. Further investigation is necessary to thoroughly grasp the processes behind these connections and to explore how significant marijuana consumption impacts elderly groups, taking into account aspects like strength.”
Subsequent investigations ought to tackle these constraints by incorporating a wider array of participants and adopting long-term studies to monitor alterations in the brain over extended periods. Research dedicated to frequent cannabis consumers and analyzing the impacts of various types and strengths of cannabis might offer a deeper comprehension of its influence. Additionally, probing gender-based disparities, as hinted at in this investigation, could uncover significant knowledge.
“Ishrat mentioned that the primary objective is to investigate how cannabis affects older individuals, broadening our knowledge beyond what has been documented in younger cohorts. This study seeks to illuminate cannabis’s influence on mental well-being, thereby offering crucial information to shape public health strategies and support policy decisions based on solid evidence.”
The study, “ Association between cannabis usage and alterations in brain structure and function: an observational and Mendelian randomisation investigation ," was written by Saba Ishrat, Daniel F. Levey, Joel Gelerntir, Klaus Ebmeier, and Anya Topiwala .